German Published Patent Application No. 40 23 828 discusses a fuel injector and a method of adjusting a fuel injector. To adjust the amount of fuel to be delivered during the opening and closing operation of the electromagnetically operable fuel injector, a magnetically conductive material, e.g., in the form of a powder which alters the magnetic properties of the internal pole is introduced into a blind hole, and thus the magnetic force is varied until the actual measured flow rate of the medium corresponds to the predetermined setpoint flow rate.
Similarly, German Published Patent Application No. 40 23 826 discusses the insertion of an equalizing bolt into a blind hole of an internal pole including a recess on its periphery, inserting it to the extent that the actual measured amount corresponds to the predetermined setpoint amount, and thus varying the magnetic force until this is achieved.
German Patent Published Application No. 195 16 513 also discusses a method of adjusting the dynamic flow rate of a fuel injector. In this case, an adjusting element situated close to the magnetic coil outside the flow path of the medium is adjusted. In doing so, the size of the magnetic flux in the magnetic circuit, and thus the magnetic force, changes, so it is possible to influence and adjust the flow rate. The adjustment may be performed with when the fuel injector is either wet or dry.
German Patent Published Application No. 42 11 723 discusses a fuel injector and a method of adjusting the dynamic flow rate of the medium of a fuel injector, in which an adjusting sleeve including a longitudinal slot is pressed into a longitudinal bore in a connection piece up to a predetermined depth, the dynamic actual flow rate of medium of the injector is measured and compared with a setpoint flow rate of medium, and the pressed-in adjusting sleeve which is under a tension acting radially is advanced until the actual measured flow rate of the medium matches the predetermined setpoint flow rate of the medium.
In German Published Patent Application No. 44 31 128, to adjust the dynamic flow rate of medium of a fuel injector, the valve housing undergoes deformation due to the action of a deformation tool on the outer perimeter of the valve housing. This changes the size of the residual air gap between the core and the armature, and thus the magnetic force, so that it is possible to influence and adjust the flow rate of medium.
One disadvantage of the group of methods which influence the magnetic flux in the magnetic circuit is the great expense with regard to manufacturing costs, because the required static flow tolerances must be guaranteed, although this is difficult to implement. In particular, measurements of magnetic fields are complicated to perform and usually require cost-intensive methods and a test field.
It is believed that a disadvantage of the group of mechanical adjustment methods is the high degree of inaccuracy to which these methods may be subject. Furthermore, the opening and closing times of a fuel injector may be shortened only at the expense of electric power, so that the electric load on the components is increased, and the controllers are under greater stress.
In particular, the method referred to in German Published Patent Application No. 44 31 128, where the residual air gap between the core and the armature is varied by deformation of the valve housing, permits only a very inaccurate correction of the flow rate because shear stresses in the nozzle body may have a negative effect on the direction and size of the deforming force. Therefore, a high manufacturing precision is necessary for all parts.